Surveillance cameras are commonly directed to move at high speed so they can identify and track a potential intruder as early as possible. However, it has been found that very slow moving threats are not always detected by some surveillance cameras because they are not capable of operating at very slow tracking speeds, and because slow speed operation presents unique technological challenges to produce recognizable images. Motorized panning and tilting of surveillance cameras at a wide range of speeds require motors that can operate smoothly at both high and low speeds. While high speed operation can effectively use brushless motors in block commutation modes, low speed operation using the same mode can degrade the quality of the image due to the lower frequency of the stepping function. This is especially apparent when a camera is panned or zoomed to follow a target that has a large down range movement as opposed to a large movement across the horizon. Fine movements of a slow-moving camera that are not smoothed out can cause noticeable stuttering and vibration that create blurring or misinterpretation of surveillance images. There is a need for a surveillance camera motion control system that operates smoothly at both high and low speeds, and does not require expensive digital encoding methods to enable smooth and precise motor control timing at low speeds. Some attempts to solve this problem have been found in the prior art and will now be described.
One prior art attempt to solve this problem is a controller used for a variable speed fridge compressor (U.S. Pat. No. 7,102,306). While both high speed block commutation and low speed sine commutation are used to provide a wider speed range, the smoothness of low speed operation is not sufficient to operate long range surveillance cameras. Another prior art attempt to solve this problem is a controller used for a variable speed dentist drill (U.S. Pat. No. 6,091,216). Again, both modes are used to provide both speed ranges, but the speed variation at slow speed ranges is not sufficient to prevent blurred images for long range surveillance camera control applications. In summary, there is still a need for a Brushless Motor Speed Control System which provides a sufficiently smooth operation for consistently clear long range surveillance imaging when used at low speeds, but is also capable of high speed camera movement when needed, and which combines these elements efficiently, at low cost, and with fewer extraneous components.